Marconi's next effort was to make it possible to send any number of messages at one time. This led to his system of tuning the sending and receiving instruments. With this system the receiving instrument will take a message only from a sending instrument with which it is in tune. It is possible, therefore, for any number of wireless-telegraph stations to operate at the same time, the waves crossing one another in all directions without interfering, each receiver responding to the waves intended for it. An ocean steamer can, with the tuned system, send one message and receive another from a different station at the same time. Marconi's ambition was to send a wireless message across the Atlantic. Quietly he made his preparation, building at Poldhu, Cornwall, England, a more powerful transmitter than had yet been used. At noon on the 12th of December, 1901, he sat in a room of the old barracks on Signal Hill, near St. Johns, Newfoundland, waiting for a signal from England. His assistants at the Poldhu station were to telegraph across the ocean the letter "S" at certain times each day. On the table was the receiving apparatus, made very sensitive, and including a telephone receiver. A wire led out of the window to a huge kite, which the furious wind held four hundred feet above him. One kite and a balloon used for supporting the antenna had been carried out to sea. He held the telephone receiver to his ear for some time. The critical time had come for which he had worked for years, for which his three hundred patents had prepared the way, and for which his company had erected the costly power station at Poldhu. Calmly he listened, his face showing no sign of emotion. Suddenly there sounded the sharp click of the tapper as it struck the coherer. After a short time Marconi handed the telephone receiver to his assistant. "See if you can hear anything," he said. A moment later, faintly and yet distinctly, came the three little clicks, the dots of the letter "S" tapped out an instant before in England. Marconi's victory was won. A flying-machine can be equipped with a wireless-telegraph outfit, so that a man can telegraph while flying through the air. Two men are needed, one to operate the flying-machine, the other to send the telegraphic messages. This has been done with the Wright machine and with some dirigible balloons. Of course, the wireless instruments on the flying-machine cannot be connected to the ground. Instead of the ground connection there is a second antenna.--one antenna on each side of the spark-gap. While in the ordinary wireless instruments the discharge surges back and forth between the antenna and the earth, in the flying-machine wireless the discharge surges back and forth between the two antennæ. In the Wright machine, when equipped for wireless telegraphy, the two antennæ are placed one under the upper plane, the other under the lower plane of the flying-machine.